1. Field of the Invention
The present invention relates to a system for interconnecting stackable housings containing electronic equipment and more specifically to an inter-unit coupling mechanism which joins individually housed computer units together both mechanically and electrically by actuation of a single actuator mechanism.
2. Prior Art
It has been common practice in the computer field to add peripheral equipment to a central computer in order to enhance the computer's operational features. For example, when additional storage is required, storage expansion units such as a disc drive, an optical storage drive, a tape drive, or additional RAM are connected to a peripheral expansion bus extending out of the computer unit's housing. The computer may then communicate with the added peripherals using a standard interface such as the SCSI (Small Computer Standard Interface) bus which has been proposed as a standard computer systems interface link for microcomputer systems.
Ribbon cables are generally connected by hand between each peripheral unit housing or box to form a daisy chained interface expansion bus such as shown in FIG. 1. The housings are typically stacked one above the other and then held in place while the interconnect cables are attached manually. One hand secures the uppermost housing while the other hand plugs the ribbon connector ends into their respective mating connectors on the housings. This manual interconnection method is adequate for situations where an expansion bus is formed only once and maintained as a permanent hardware extension at a single computer site. In large computing environments such as large offices where a plurality of central processing units are located at different sites it may be desirable to purchase only one storage expansion unit and utilize it on a shared basis by moving it from one central processing site to the next as needed. This will occur for instance when a local area network (LAN) linking the various central processing sites is not available. It will also occur in situations where the storage expansion unit is a high density device such as a 100 Mbyte optical storage drive whose use is optimized by connecting to a central processing unit using a short length cable capable of transferring data at high speed.
In these situations where a single expansion unit is shared by moving it from site to site, the expansion bus connectors are repeatedly connected and disconnected at each computer site. A reliable interconnection system is required in order to avoid system failure after each connect/disconnect operation.
Manual interconnection does not provide adequate safeguards because it gives the user unlimited freedom and thereby enables an unlimited number of failure modes. If for example, the connectors of the manual interconnect system are not fully mated when plugging one connector into another, one or more expansion bus lines may be left open thereby causing system failure. Untrained users often pull on the wires rather than the connector ends of an interconnect cable when unplugging one unit from another and this places excessive stress on the cable wires which then tend to break away from the connector pins inside the connector ends of the cables to create an intermittent open circuit which is difficult to diagnose. The manual interconnect method does not limit the length of cable used to connect one unit to the next. Long cables tend to generate undesirable EMI (electromagnetic interference) particularly when the cables in the conventional interconnect system are not properly shielded. Because the cables in the conventional system are detachable at both ends, special attention is required to make sure individual cables are not lost when peripheral units are rearranged (e.g., when transporting peripheral units to other computer sites).
The conventional arrangement shown in FIG. 1 is formed by placing one peripheral unit or box on top of the other and manually plugging interconnect cables in daisy chain fashion between the units. Each of the three boxes 10, 20, 30 shown in FIG. 1 includes an AC power switch 11, 21, 31 and a UL approved power connector 12, 22, 32 for safely providing high voltage AC power to the respective individual boxes 10, 20, 30.
Referring first to the base unit 10, a fifty pin SCSI bus connector 13 is fixed to the rear face of the base unit housing and a cover plate 14 is provided over an optional connector hole in the rear face of the housing. The rear face of the base unit housing also includes ventilation holes 15 for forced air cooling. A power supply housed inside the unit provides DC power to circuit boards inside the housing. Four rubber feet 16 support the base unit above a base surface such as a desk top and protect the base surface from scratching.
The second unit 20 rests above the base unit 10 on four rubber feet 26 and has a rear face plate identical to that of the base unit 10 with the addition of a second expansion bus connector 24 provided below the first expansion bus connector 23. Correspondingly numbered parts of the second unit 20 are identical to the parts already described with reference to the first unit 10 and their description is therefore omitted. Similarly, correspondingly numbered parts of the third unit 30 are identical and need not be described further.
An interconnect cable 40 provided with end connectors 41, 42 at opposed ends links the expansion bus connector 13 of the base unit to the expansion bus connector 24 of the second unit. The ends of the interconnect cable are manually plugged into respective mating connectors 13, 24 by "jiggling" the end connectors 41, 42 while applying a manual insertion force until the user feels that the end connectors are properly seated in their respective fixed connectors 13 and 24. Typically, an insertion force of at least twelve pounds is required for mating fifty pin connectors such as those used on the SCSI bus. This insertion force is even larger when the connectors are not accurately aligned. If the connectors are grossly misaligned and excessive force is applied, the connector pins will be damaged.
When the third unit is added to the stack, one hand holds the third unit 30 which is supported by four rubber feet 36 on top of the second peripheral unit 20 while the other hand is used to repeat the above plug-in procedure for the second and third units. End connectors 51, 52 of interconnect cable 50 are press fit into expansion bus connectors 23, 34, respectively, with the cable 50 then forming a loop extending outwardly from the rear of the stack. A third cable 60 links the daisy chain arrangement to a host computer through its end connector 61 which mates with fixed connector 33.
Disconnection is performed in a similar but reverse manner. One hand secures the topmost unit that is being removed from the stack while the other hand grasps the end connector and wiggles it out of the fixed connector on the unit housing. All too often the wire portion of the interconnect cable is pulled to unplug the end connector, placing excessive strain on the cable wires and potentially loosening them from their connection to the cable connector terminals thereby creating the intermittent open circuit discussed above.
In addition to the cables shown in FIG. 1, three AC power cords (not shown) extend from the rear power connectors 12, 22, 32 to a multiple outlet power strip (not shown). Space is therefore required beyond the rear face plates of the peripheral units for the numerous interconnect cables, power lines and the multiple outlet strip mentioned. This bundle of cables extending from the rear of the stack detracts from the stack's overall aesthetic appearance and uses space which could otherwise be available behind the stack.
The cable bundle extending from the rear surface of the stack also increases the danger of accidental damage to the peripheral units because one of the outwardly projecting cables at the rear of the stack can be snagged during routine maintenance, such as when cleaning the exterior surface of a unit. The snagged cable may pull the units to which it is connected off their resting positions on the stack and possibly damage connector pins in the process. From the above discussion it can be seen that this loose arrangement of units stacked one on top of the other with separate detachable cables extending from their rear surfaces suffers numerous drawbacks.
Incidentally, there is one more problem created by the interconnect system shown in FIG. 1 which is never considered until the stack is powered up and operating. A user wishing to add or remove a unit from the stack is confronted with three power switches, 11, 21, 31 and a bewildering number of choices. It is not clear to the user whether all the power switches should be shut off before adding a unit, only one switch should be shut off, the cable connectors should be mated/uncoupled first before turning power off, or the power should be shut off first before mating/uncoupling the connectors. Even experts can be baffled by the variety of choices.